Micromanometer



um WHIHMHHHHH will lf l i il W. 5- YOUNG MICROMANOMETER Filed May 11, 1946 Nil m 1mm min IN V EN TOR.

Willi You BY f Patented May 30, 1950 UNITED STATES fPATEN-T oer-ice .fi'atoasz'z William s. Young, Philadelphia, Pa, minor to The Atlantic Refining Company, Philadelphia, Pa., a corporation of Pennsylvania Application May 11, 1846,.Serial No. 669,040 10 Claims. (01. 73-401) The invention relates to improvements in devices adapted for the measurement of low pressures, and more particularly for the measurement of small changes in pressures at very low pressures.

In the ordinary manometer designed to measure pressures at substantially atmospheric pressure, mercury can be utilized satisfactorily due As a result of its great density and high surface tension, mercury will not react to small changes in pressure in such a way as to permit sufficientlyaccurate measurements. In such a situation, liquids having low density and surface tension have been found to be eminently satisfactory 8 p e ing measured, and will also tend to adulterate such sample.

One of the objects of the invention, therefore, is to provide a micromanometer which will accurately measure low pressures or changes in pressure at relatively low pressures.

Another object of the invention is to provide a micromanometer in which liquids having a low density and surface tension can be used without volatilization thereof.

Other objects of the invention will be apparent from the description and claims which follow.

In the drawing like numerals are used to designate like parts.

The figure shows a front elevational view of the device which is shown as fabricated of glass.

In the drawing, l and 2 are vertically arranged U-tubes preferably having a length between 700 and 760 mm. Afilxed to the ends of the shorter arms of said tubes are lower reservoirs 3 and I respectively, the diameter of said lower reservoirs being relatively larger than the diameter of said tubes. Capillary tube 5 connects the upper portions of said lower reservoirs.

Inlet tube 6 is connected to capillary tube 5 and controlled by three-way stopcock 1, .such

stopcock providing controllable means of communication with supply reservoir 8 and air inlet 8, the latter being controlled by stopcock I0.

fsides of lower reservoirs 3 and 4. -15

sired to measure.

tube '22 through which mercury can be intro.

. z ends of the longer arms of U-tubes I and 2 respectively, the diameter of said upper reservoirs being relatively larger than the diameter of said tubes. Said upper reservoirs are provided with elongated necks l3 and M respectively, to which are attached stopcocks l5 and I6 respectively. These stopcocks are of the hollow plug variety, the plug walls I! and i8 respectively being aperturecl at H and 20 respectively, and

the bottom of the plugs being open. to provide communication with elongated necks l3 and M respectively. Stopcock I5 is provided with side arm- 2| through whichconnection is made with a vessel, the pressure of whose contents it is de- Ailixed to neck i3 is inlet duced into the 'micromanometer, as will be de-' scribed in detail hereinafter. Horizontal tube 23 affords communication between neck l3 of upper reservoir II and stopcock l6 affixed to neck ll of upper reservoir l2.

In preparing the micromanometer for operation, stopcocks l5 and ii are opened and stopcocks I and ID are closed. The micromanometer is then evacuated by connecting stopcock side arm ill to a suitable vacuum pump, such as a mechanical pump or a mercury vapor pump (not shown). In order to remove air adsorbed on the walls of the device, such walls may be heated with a flame or a hot air gun, precautions being taken to protect the various stopcocks. Stopcocks l5 and ii are then closed ensuring a continued vacuum within the device. Mercury is distilled into the micromanometer through inlet tube 22 until the levelof the mercury is approximately even with the bottom of the upper reservoirs and inlet tube 22 is sealed oil as at 24, for example by the application of flame.

A suitable liquid, which has been thoroughly degassed, is'admitted through stopcock I from supply reservoir 8 into capillary tubei until the nterface between the mercury and the liquid stands approximately halfway up the vertical density and surface tension and its ability to but any liquid conforming to the aforementioned requirements can be used. .As a result of the admission of liquid and the consequent displace-' ment of mercury in the lower reservoirs, the meniscus of mercury in the upper reservoirs will stand approximately halfway up the 'vertical Upper reservoirs i l and I2 are affixed to the-- B5 sides of said upper reservoirs.

The suitability. L, of the liquid for such purpose consists in its low tion of such bubble can be adjusted in relation to a small scale (not shown) associated with said capillary tube by the addition ,or withdrawal oi liquid. It will readily be understood that, if so desired, the scale itself can be moved in relation to the bubble.

The operation of the device is as follows:

When it is desired to measure the pressure of a gas, side arm 2| of stopcock II is connected with a vessel containing the gas. stopcock II is then opened and communication is made between neck I3 of upper reservoir II and the vessel containing the gas. The resulting increase in pressure on the surface of the mercury in upper reservoir ll results in a downward displacement l vSensitiv ty 8- -Where 1 is the bubble displacement in mm. and

P is the applied pressure in mm. of mercury.

Setting up a datum plane at A--A in the figure,

and dividing the micromanometer into two halves by 3-15, the left half being denoted by subscripts i and the right half bysubscripts 2, the micromanometer at equilibrium after evacuation satisfies the following relation:

where P is the residual pressure acting on the upper reservoirs after evacuation.

H is the head of the mercury above the datum plane h is the head of pentane above the datum plane pm is the density of mercury pp is the density of n-pentane, all in consistent units. Let an unknown pressure P be applied to left hand reservoir, then I Assuming incompressible fluids, the volume transferred from the reservoirs due to the change in head must equal the volume transferred through the capillary tube 1. e.

AHA=la where A is the area of the reservoirs a is the area of the capillary tube l is the linear movement of the bubble.

AHarD ll'i where D is the diameter of the large reservoirs 4 d is the diameter of the capillary tube ing and substituting 4 in 8 a d P=2l (2-:)+A, Solving for the sensitivity Defining the manometer constant, C, in terms of dimensions and physicalproperties:

Substituting in 6 the values,

rearrangv d=0.126 cm.

the

D=8.10 cms. m=13.534 g./cc. at C. pp=0.6213 g./cc. at 25 C. C=1056 It will be understood that the dimensions and densities given above merely represent an example and the scope of the invention is not to be considered as limited thereto.

Substituting the constant in 5 The negligible effect of the A term on sensitivity can be shown by the following example:

Assume the pressure P to be measured is microns and that the residual reference reservoir pressure P2 amounts to 10 microns. P2 will change according to the relation (7) I P2V=(P2+Ap) (V-AV) where V is the original reference reservoir volume and, AV is the change in the reference reservoir volume caused by the applied pressure P.

But, I AV=AHA Substituting in '7 and rearranging P,V o 5 V Am Assuming a valuefor V of cc. and solving AP==6.43 X 10- mm.

and

thus, less than 0.013% change in sensitivity would result from 10 microns residual pressure in upper reservoir l 2. Similarly it can be shown that a reference reservoir pressure of 780 microns would be required to change the sensitivity by 1 Hence, for all practical purposes, this factor can be disregarded and the sensitivity regarded as equal to the manometer constant.

S=1056 therefore,

.Jlvertically arranged U-tubes each having a long leg and a short leg, reservoirs connected to the ends of said legs, anda capillary tube connecting the reservoirs on the short legs.

2. A micromanometer, comprising a pair of vertically arranged U-tubes each having a long leg and a short leg, reservoirs having a diameter greater than said legs connected to the ends of said legs, a capillary tube connecting the reservoirs on the short legs, and valve means connected to said capillary tube.

3. A micromanometer, comprising a pair of vertically arranged U-tubes each having a long leg and a short leg, reservoirs having a diameter greater than said legs connected to the ends of said legs, a capillary tube connecting the reservoirs on the short legs, valve means connected to said capillary tube, and means associated with the aforesaid elements to measure the pressure of a fluid introduced into said micromanometer.

it. it micromanometer, comprising a pair of vertically arranged iJ-tubes, each having a long leg and a short leg, reservoirs having a diameter greater than said legs connected to the ends of said legs, a capillary tube connecting the reservoirs on the short legs, valve means connected to said capillary tube, and means contained within said capillary tube to indicate the pressure of a fluid introduced into said micromanometer.

5. A Inicromanorneter, comprising a pair of vertically arranged U-tubes each having a long leg and a short leg, reservoirs having a diameter greater than said legs connected to the ends of said legs, a capillary tube connecting the reservoirs 'On the short legs, valve means connected to said capillary tube, an index bubble contained within liquid in said capillary tube, and valve means associated with the reservoirs on the long legs.

6. A micromanometer, comprising a pair of vertically arranged U-tubes each having a long leg and a short leg, reservoirs having a diameter greater than said legs connected to the ends of said legs, a horizontal capillary tube connecting the upper portions of the reservoirs on the short legs, valve means connected to said capillary tube, an index bubble contained within liquid in said capillary tube, and valve means associated with the reservoirs on the long legs.

7. A mlcromanometer, comprising a pair of 8. In a micromanometer, comprising a pair of vertically arranged U-tubes each having a long leg and a short leg, reservoirs connected to the ends of said legs, and a capillary tube connecting the reservoirs on the short legs, pressure indicating means, comprising mercury columns contained within said legs and partially filling said reservoirs, and a liquid having a relatively low viscosity and surface tension contained Within said capillary tube and partially filling said reservoirs on the short legs, and an index bubble contained Within the liquid in said capillary tube.

9. In a micromanometer, comprising a pair of vertically arranged IlJ-tubes each having a long leg and a short leg, reservoirs having a diameter greater than said legs connected to the ends of said legs, and a capillary tube connecting the reservoirs on the short legs, pressure indicating means, comprising mercury columns contained within said legs and filling said reservoirs to the extent of about one half the volume thereof, a liquid having a relatively low viscosity and surface tension contained within said capillary tube and iilling said reservoirs on the short legs to the extent of about one half the volume thereof, and an index bubble positioned in said liquid.

10. In a microinanorneter, comprising a pair of vertically arranged U-tubes each having a long leg and a short leg, reservoirs having a diameter greater than said legs connected to the ends of sand legs, and a capillary tube connecting the reservoirs on the short legs, pressure indicating means, comprising mercury columns contained within said legs and filling said reservoirs to the extent of about one half the volume thereof, normal pentane contained within said capillary tube and filling said reservoirs on the short legs to the extent of about one half the volume therevertically arranged U-tubes each having a long leg and a short leg, reservoirs having a diameter greater than said legs connected to the ends of said legs, a horizontal capillary tube connecting the upper portions of the reservoirs on the short legs, valve means connected to said capillary tube, an index bubble contained within liquid in said capillary tube, valve means associated with the reservoirs on the long legs, a tubular element oonnectingsaid reservoirs on the long legs, and means adapted to admit fluids into one or said reservoirs on the long legs and said tubular element.

of, and an index bubble Positioned in said pentane.

WILLIAM S. YOUNG.

REFERENCES CITED The following references are of record. in the file of this patent:

UNITED STATES PATENTS Number Name Date 949,598 Roberts Feb. 15, 1910 1,637,653 Nordenson Aug. 2, 1927 2,051,740 Palkin Aug. 18, 1936 FOREIGN PATENTS Number Country Date 19,426 Germany Oct. 3, 1882 OTHER REFERENCES Pages 91 to 103 inclusive 0! Bulletin No.

or theUniversity of Illinois. Engineering Experiment Station. dated March, 1921. 

